Mechanical latch relays are usually employed where it is desired to initially operate the relay contacts by energizing an associated electromagnet, and then retaining the contacts in their operated state with a mechanical latch. The electromagnet can then be deenergized and there is no power consumption during the period of operation. When it is desired to restore the relay contacts to their initial, unoperated state, a secondary electromagnet is energized to trip the mechanical latch.
Mechanical latch relays are particularly suitable for controlling apparatus that is run continuously over long time periods, such as fans and pumps. The apparatus can be run without requiring constant electrical operation of the primary electromagnet in the relay.
These latching relays also provide a memory function for control circuits. Where a number of relays are employed in a control circuit, the probabilities at any given moment are that some of the relays are energized and "closed," and some of the relays are deenergized and "open". In the event of an interruption, a power failure for example, it is sometimes desired to maintain the relays in the open or closed state which they were in prior to the interruption. This simplifies restarting the controlled apparatus because it eliminates the need to reset relays to obtain a particular operating point in the control cycle.
Still another application for these latching relays is in areas where low noise levels must be maintained. If the hum or chatter of an energized electromagnet is objectional, a mechanically-held relay is sometimes the solution to the noise problem.
The mechanical latch structure of these relays usually is an accessory or adjunct to an electromagnetic relay of standard design. By attaching the mechanical latch structure, the conventional relay is converted to a mechanical latch relay. As an attachment, the mechanical latch mechanism provides increased versatility to an existing electromagnetic relay.
Because a mechanical latch device is usually an attachment for an existing electromagnetic relay, it should be compatible with this relay. It should also be interchangeable with other attachments for the relay. For example, a timer attachment that provides time delayed switch operation may be another attachment for the basic relay, so that either the mechanical latch attachment or the timer attachment may be mounted to the basic relay to provide the desired optional features. The mechanical latch attachment and the timer attachment should preferably be mounted on, and connected to, the basic relay in a similar manner. It would also be preferable to have a mechanical latch attachment and a timer attachment with common and interchangeable subassemblies and parts, to simplify manufacture of the two devices.
The known prior art does not disclose a mechanical latch mechanism that has subassemblies and components that are common to, and interchangeable with, the subassemblies and components of a timer mechanism. Another characteristic of the prior devices is an integral construction in which it is inconvenient to remove some components for inspection or servicing.
Because the latch mechanism in a mechanical latch relay may be operated many thousands of times, the latch mechanism must be resistant to wear that would impair its ability to latch. Several prior art devices have employed latch mechanisms that are constructed with hardened metal parts. These metal parts are relatively expensive to manufacture in comparison with parts that can be molded from thermoplastic resinous materials or other non-metallic materials. A problem in producing a latch mechanism with molded plastic parts has been providing the service life and smooth operation that is required in an industrial control relay. One prior device with a non-metallic latch mechanism includes a latch and a catch with squared-off corners on their mutually engaging surfaces. These corners, however, tend to become rounded after a moderate number of operations, thereby increasing the opportunity for a failure or miss by the latch mechanism.
Mechanical latch relays, like other relays, are often mounted in control panels and relay banks where mounting space is limited, and it is therefore important that requirements for additional mounting space for the mechanical latch mechanism be minimized. Because mechanical latch mechanisms include secondary electromagnets, more compact devices are not easily obtained. Prior mechanical latch relays have been assembled in at least two general configurations. In one configuration, a mechanical latch attachment is stacked on top of the control relay and fastened to it, the control relay forming a base for the mechanical latch attachment. In another configuration, the mechanical latch mechanism is mounted to the side of a portion of the relay that houses the primary electromagnet. This side by side configuration presents a disadvantage where mounting space for the relay is limited.
In some applications, a latching relay should be capable of both manual and electrical operation to both close and open a circuit. In other applications, manual operators are important because they allow the relay to be periodically tested. These manual operators should be easy to reach and operate when the relay is mounted in a control panel or relay bank. It is not believed that any of the devices of the "stack" configuration mentioned above include both a manual latching operator and a manual release operator located on a top or forward portion, and operable with a pushing or depressing motion.